the following image was kindly provided by the protease and protease inhibitor web server prolysis.

Alpha-1 Proteinase Inhibitor is an inhibitory member of the serpin superfamily in the cleaved conformation. Serpins share a common tertiary structure with three beta sheets and nine alpha helices. The inhibitory reactive site forms an exposed loop whith the P1-P1' residues acting as a bait for the target protease. The interaction with the protease leads to the formation of an irreversible serpin-enzyme complex, which is further cleaved at the P1-P1' peptide bond. After this cleavage, the central beta sheet (coloured white) undergo a considerable refolding since the P15-P1 region is incorporated in the central beta sheet where it forms a new strand (s4A coloured red here). In the cleaved conformation, the P1 residue (Met358) is separated from the P14 residue (Ser359) by 70Å (mono).